The present invention relates to a process for the preparation of iron nitrosyl carbonyl.
The complex, iron nitrosyl carbonyl [Fe(NO).sub.2 (CO).sub.2 ], is known to dimerize butadiene to produce vinyl cyclohexene (VCH). Methods known to prepare various iron nitrosyl complexes require reduction of [Fe(NO).sub.2 Cl].sub.2 or reaction of nitric oxide (NO) on a mixture of iron and FeCl.sub.3. Reference to these methods is found in U.S. Pat. No. 4,238,301. Another patent, U.S. Pat. No. 4,234,454, discloses the preparation of various metal nitrosyl catalytic solutions by employing the combination of manganese, zinc or tin together with iron, cobalt or nickel nitrosyl halides to produce the respective metal nitrosyls in a system for dimerizing various conjugated dienes. An earlier patent, U.S. Pat. No. 3,510,533, discloses the dimerization of conjugated dienes with .pi.-allyldinitrosyliron complexes and a method for their preparation. Several methods are given involving the reduction of a .mu.,.mu.'-dihalotetranitrosyldiiron.
The dimerized products of the process of the invention may be useful in themselves or as intermediates to other products. Thus, for example, 4-VCH can be (1) chlori-nated to make an insecticide, (2) oxidized to make benzoic acid, (3) reacted with hydrogen sulfide in the presence of acid-type catalysts to make sulfur-contain-ing resins and (4) reacted with hydrogen sulfide in the presence of ultraviolet light to make a .beta.-mercaptoethyl cyclohexane.
In copending U.S. application Ser. No. 07/348,625, filed May 8, 1989, (Heaton) which is incorporated by reference herein in its entirety, Heaton has demonstrated that an iron nitrosyl carbonyl catalyst effective for dimerizing olefins can be prepared by reacting an iron, cobalt or nickel chloride and an alkali metal nitrite or an iron cobalt or nickel nitrosyl chloride with carbon monoxide (CO) in the presence of a readily oxidizable metal exemplified by tin, zinc, manganese or magnesium. Certain by-products have been observed in the product produced by such a process. The product is stable when stored under CO, but when the CO is replaced by e.g. nitrogen (N.sub.2), the concentration of Fe(NO).sub.2 (CO).sub.2 decreases.
It would be desirable to produce an iron nitrosyl carbonyl catalyst such that there were fewer by-products and more stability.